The present invention relates to electrically insulated coils and a method of manufacturing the same, and more particularly it relates to electrically insulated coils suitable for use in rolling stock traction motors, industrial rotating electric machines and the like which demand a high voltage and heat resistance, as well as moisture resistance or water resistance, and to a method of manufacturing the same.
Reflecting increasing demands for compactness and light weight required for rolling stock traction motors and industrial rotating machines in general, electrically insulated coils to be utilized in such applications are required to have a substantially improved insulation performance capable of operating at a higher voltage and at a higher temperature. On the other hand, in order to ensure an efficient utilization of energy, recent rotating electric machines do not necessarily aim at increasing the capacity but rather are moving toward a parallel operation of a plurality of small capacity machines through controlling the number of units in operation in accordance with a varying load demand.
Reflecting this background, manufacturers are increasingly pressed to develop a manufacturing method capable of mass producing in a short period of time at a lower cost a large number of small capacity rotating electric machines having electrically insulated coils capable of withstanding a higher voltage and a higher temperature.
According to prior art rotating electric machinery insulation coils as disclosed in Japanese Patent Application Laid-Open No.3-77203 (1991), an insulation substrate layer is prepared by winding an insulation tape around a conductor, which is then impregnated with an impregnation resin, and cured so as to form an insulated coil. Further, because of the recent development of an epoxide impregnation resin utilizing a multifunctional epoxy, it has become possible to provide electrically insulated coils even by utilizing epoxy resins that can be operated continuously at temperatures exceeding 200.degree. C. As for the composition of such an impregnation resin, it is typical to blend in the resin a hardener such as an acid anhydride which reacts relatively slowly.
Such impregnation resin heretofore has an advantage that its reaction progresses least while on the shelf, but through addition of a curing accelerator for use with said impregnation resin to the insulation substrate layer, the reaction of the impregnation resin is caused to speed up. Through adoption of this method, it has become possible to repeatedly apply the impregnation resin, whereby a yield of applying the impregnation resin has been substantially improved. As curing accelerators suitable to be utilized in such applications, an imidazole catalyst is employed in most cases.
On one hand, in order to manufacture small capacity rotating electric machines in a short time, it is necessary to minimize a hardening schedule for the impregnation resin thereof. For this purpose, and in consideration that the heat resistance of the insulation in the electrical insulation coils largely depends on a heat resistance of the impregnation resin itself, it was necessary to increase the curing temperature such that no insufficient hardening would result, and a predetermined heat resistance was ensured even when the hardening schedule was shortened.
However, in the case where a conventional imidazole curing catalyst was utilized as a hardener accelerator, it was necessary, when forming an insulation having a heat resistance over 200.degree. C. as set forth in Japanese Patent Application Laid-Open No. 3-77203 (1991), to conduct a slow cooling of the impregnation resin at the time of curing by following the steps of 100.degree. C. for 10 hours +150.degree. C. for 3 hours +230.degree. C. for 10 hours, wherein at the initial stage of the lowest temperature a sufficient time was spent cause the hardener accelerator to fully interact with the resin. This slow curing was necessary because of a low heat resistance intrinsic to the curing catalyst itself, even though the yield of the impregnation resin increased as aforementioned.
In this regard, the curing time which required a prolonged time exceeding 20 hours caused a bottleneck in manufacturing the rotating electric machines in a short production time.
On the other hand, lately there has been developed an addition compound type hardener obtained by addition reaction of imidazole and a resin as set forth in Japanese Patent Application Laid-Open No.3-37220 (1991), which has been conceived to solve the drawback of said imidazole curing catalyst having a low heat resistance, and a method of utilizing this hardener as a curing catalyst has been proposed.
This addition reaction product, however, which has an advantage that a greater heat resistance is ensured, nevertheless has a greater molecular weight and thus an increased melting point, and thus has a disadvantage in that it is difficult to dissolve into a solvent and a resin.
Therefore, except for such use in direct blending with a resin as set forth in Japanese Patent Application Laid-Open No. 3-37220 (1991) whereby a sufficient time for blending was afforded thereby enabling practical applications be implemented, it was impossible to apply this art, for example, to the insulation of the rotating electrical machines wherein because of repeated impregnation of the resin required, the curing catalyst could not have been mixed directly with the impregnated resin. As a result, a homogeneous reaction was not ensured inside the insulation layer, and thus it was likely to give a heterogeneous property to the insulation layer, thus precluding actual applications thereof.
On the other hand, along with the development of new insulation materials, the insulation of the electrically insulated coils in the rotating electrical machines has been improved substantially, thus greatly contributing to the improvement of reliability of the machines. In most cases, however, because induction motors for pumps, traction motors for rolling stocks and the like are used outdoors, and often in a high humidity environment, their operational environments are more stringent in comparison with typical induction motors which are installed in doors. Therefore, a high reliability with respect to moisture resistance and water resistance is required for any rotating electric machine to be utilized in such environments. In particular, the insulation of electrically insulated coils to be utilized in such applications is an important technical subject to be dealt with more extensively.
As prior art manufacturing methods for manufacturing electrically insulated coils for rotating electric machines to be applied in such environments, there are known such means and methods as disclosed in the Japanese Patent Application Laid-Open No. 58-72348 (1983), whose method comprises the steps of forming a hot melt adhesive hydrophobic insulation layer on the outer surface of the mica insulation layer, forming a thermally contracting insulation layer thereon, thereafter integrating the same into the core, and performing an integral impregnation treatment. Another method is disclosed in the Japanese Patent Application Laid-Open No. 1-122349 (1987) in its prior art section, in which rotating electric machines are manufactured having a winding provided with an insulation layer on the conductor, a core having slots to insert said winding, a groove provided in the outer peripheral portion of said slot for firmly fixing said winding, and a wedge to be inserted into said groove. After combining the foregoing members, an integral varnish impregnation is performed, and the method comprises the step of coating the wedge with a curing catalyst for curing the impregnated varnish at least on the entire portion of the surface of the wedge which is directly in contact with the core groove prior to the varnish impregnation so as to ensure prevention of outflow of the varnish, or, in the case of the electrically insulated coils manufactured by means of the integral impregnation process, the method comprises the steps of applying the varnish treatment twice, or subjecting to the rotary hardening and the like so as to provide a thicker layer of varnish which thereby serves as a hydrophobic insulation layer as well.
Further, there is also known, as disclosed in Japanese Patent Application Laid-Open No. 58-182443 (1983), to minimize the stress arising due to heat contraction in the coils contained in the slots of a huge rotor core of a rotating electric machine such as a turbine generator and to prevent plastic deformation in the coils from occurring as well, by applying a fluorine-containing coating on the surface of coils for use in the rotator of a rotating machine having coils contained in the slots of the rotor core and supported by wedges via insulation blocks in the radial direction.